United States Reissue patent No. 28,104 -issued Aug. 6, 1974 to Richard C. Grace (one of the co-inventors of the subject invention) entitled "Pump Storage Grinder" and assigned to the Environment/One Corporation, describes and claims a sewage grinder pump system that has received considerable acceptance in the industry. The sewage grinder pump system disclosed in Re. 28,104 employs a sewage collection and storage tank of about 50-60 gallon capacity having a gravity fed raw sewage inlet and removable top cover. The top cover supports a liquid-tight, sealed housing having a separately removable cover and that contains a motor and motor controls for rotating a common shaft to which both a grinder or comminutor and a positive displacement pump rotor are secured. The storage tank serves to collect both sewage and waste water from a typical single family residence until the level of sewage is sufficient to actuate a pressure sensitive electric switch. The electric switch turns on the sewage grinder pump causing it to both macerate solids entrained in the sewage and pump the ground sewage under pressure out through a discharge outlet conduit normally having a one-way check valve therein to a suitable disposal point for the pressurized liquid sewage.
This known sewage grinder pump system was initially designed for installation in basements, crawl spaces or slabs of single family residences, small office buildings and manufacturing plants, and the like, but in the intermin has been used in many installations where it has been buried outside, in the backyard of a home for example. In some instances it is necessary to bury the sewage collection tank to a depth below the normal grade or surface of the ground thereby necessitating the installation of a large diameter manway that is substantially the same cross-sectional dimension (or greater) than the sewage collection tank such as disclosed in U.S. Pat. No. 4,014,175, issued Mar. 29, 1977. The large diameter manway is used because it was an easy and direct extension of the surface unit and may or may not employ guide rails for lowering and raising the sewage grinder pump unit together with junction boxes, shut-off valves, disconnect means and the like. In order to accommodate these parts and to allow access to the sewage grinder pump for removal, repair and maintenance or replacement, the large diameter manway is necessary. In some installations, the required manway can be as deep as 2-10 feet below ground, thus necessitating the installation of a rather extensive and costly manway facility.
In the above briefly-described, known sewage grinder pump system, the electric motor for the grinder pump and its controls are supported within a liquid-tight housing which normally is above the highest level of liquid sewage allowed to collect in the tank by the level sensing switch used to control the grinder pump motor. The drive shaft driven by the electric motor extends down through a suitable shaft seal to drive the pump rotor and comminutor-grinder that are secured to the shaft and are disposed within the liquid sewage collected in the tank. Thus, in effect, this known sewage grinder pump constitutes an over and under dry well/wet well type of arrangement.
Combined dry well/wet well pumping systems are old in the art and have long been used in pumping both storm sewage as well as waste sewage. In these older arrangements, two wells are driven side by side into the round, one of which is maintained dry and the other of which serves to collect the liquid to be pumped. Such wet well/dry well systems are described in the "Submersible Sewage Pumping Systems Handbook" published by Lewis Publishers, Inc., 121 South Main Street, PO Drawer 519, Chelsea, Michigan 48118 USA, published 1986. For a more detailed description of the parallel, wet well/dry well arrangement reference is made to the above-noted handbook. Only a cursory comparison is required, however, to appreciate that the digging or driving of two pits to accomodate a wet well/dry well, is complex and costly, and has greater impact on the environment than the driving of a single well system.
In addition to the above two briefly described systems, the industry has further developed a single wet well system which employs submersible pumps, a description of which appears on pages 4 and 5 of the above-noted "Submersible Sewage Pumping systems Handbook". Submersible pump wet well sewage systems have found acceptance, particularly in the larger rated system, but require the building of an enlarged manway to accommodate the guide rail structure used with such systems, along with necessary junction boxes, shutoff valves, disconnect mechanisms and the like.
The guide rail structure is a standard component of a single wet well submersible pump system. The rails, usually are spaced-apart galvanized pipes and are mounted in place from the bottom of the wet well to the access cover. A bracket on the pump unit mates with the rails so as to properly support the pump when it is in place at the bottom of the wet well and to resist torque by the sewage pump motor while operating. During initial installation, the submersible pump or pumps are lowered into place on the guide rails and fitted to a discharge pipe by means of a quick connect-disconnect mechanism. The guide rail structure normally is a substantial, component part of a submersible pump type wet well and takes up a lot of space in the well so that an accessway comparable in cross-sectional dimensions and size to the collection tank is required.
A hoist normally is used to install the pump or to remove the pump for inspection or servicing. The hoist may be a portable hoist, truck mounted or be a permanent part of the wet well installation. A chain or cable is attached to a bracket on the top of the submersible pump, and the pump is lifted into or out of the well while being guided by the guide rails. During removal a sealing flange on a quick connect-disconnect coupling mechanism disengages from the discharge pipe so that the submersible pump can be raised to the top of the well guided by the guide rail system. After inspection and servicing, or upon initial installation, the submersible pump is lowered back into the wet well along the guide rails so that the sealing flange of the quick connect-disconnect coupling automatically engages the discharge pipe and the system is ready for operation. The guide rail system also must be designed to resist the torque developed by the submersible pump during operation so that it is necessarily strong and bulky.
To overcome the above briefly-discussed problems of pressurized sewage disposal installations which are to be buried in the ground outside the facility which they serve, the present invention was devised.